Is it real to get an IP PBX installation for as little as 8 Euro a month? Yes, when using cloud platform. But surprising result we’ve got in out testing is that Asterisk installed on smallest virtual server VQ7 of Hetzner (1 virtual CPU, 512 MB RAM, 20GB HDD), 8 Euro/ month, can stand the load of 70 concurrent users

1. IP PBX Asterisk ® cloud installation
load testing
Evgeny Anvaer, Vladimir Dudchenko, Dmitry
Komov
SoftBCom, Ltd. (www.softbcom.ru)
12.04.2014

2. IP PBX Asterisk ® cloud installation
load testing: the task and results
• Is it real to get an IP PBX installation for as little as 8 Euro a
month? Yes, when using cloud platform. But surprising
result we’ve got in out testing is that Asterisk installed on
smallest virtual server VQ7 of Hetzner (1 virtual CPU, 512
MB RAM, 20GB HDD), 8 Euro/ month, can stand the load of
70 concurrent users.
• We successfully use such an installation for a few months.
But our load test outlined below confirms the fantastic
throughput level of such an installation.

3. Testing methodology
Below is the usual scheme of IP PBX load creation:
Definitely, it is an embarrassing to generate more than 20 concurrent calls
in such a way, using manual dialing.

4. Real load testing approach
For load generation the Wombat Dialer™ system (http://wombatdialer.com/) was
used. It was kindly presented us by Swiss company Loway.
Wombat Dialer is designed for automated ringing round big number of customers.

5. The load generation and measurements
The calls from local Asterisk on the scheme above were forwarded to the tested
Asterisk server, which was making connections, and then playing back music into
the line. Tested server recorded all the calls. The number of concurrent test calls
was set in Wombat Dialer.
The number of concurrent calls Peak CPU usage in tested
asterisk
Peak RAM usage in tested
asterisk
Quality of hearing
10 10% 4,3% Excellent
20 19% 4,6% Excellent
30 26,9% 4,7% Excellent
40 35,2% 5% Excellent
50 43,2% 5,3% Excellent
70 59,1% 5,8% Excellent
90 76,7% 6,5% Excellent
100 76,7% 9,9% Good
105 79,4% 9,4% Noticeable distortions
126 81,4% 9,5% Hard distortions

6. CPU load dependency
from the concurrent calls number
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
0 20 40 60 80 100 120 140
As the CPU load level was permanently varying, only maximum values achieved
in the 2 minutes interval (duration of testing session) were included into the
measurements results. In repeated testing sessions the deviation of the values
was in the range of 5% – 10%

7. The conclusion: the cloud Asterisk installation
can stand about 70 concurrent calls
• In direct measurements cloud installation of IP PBX Asterisk
demonstrated capability to serve up to 90 -100 concurrent calls.
• Considering influence of systematic errors (in our case the tested
Asterisk didn’t make outbound calls) and accidental dispersion of
registered values it is necessary to apply margin level of approximately
25%-30%.
• The result: the load limit in reality should be set at the level of
somewhat 70 concurrent calls.
• Definitely this result is only a kind of estimation, and shouldn’t be
treated as a “firm” recommendation.
• For the cases when the planned load level of production system
exceeds half of upper limit outlined above we would propose setting a
CPU load monitoring with alerting for threshold of 60 -70% or so - for
real load control.